1. Field of the Invention
This invention relates to a vacuum circuit breaker, and more particularly to a vacuum circuit breaker chiefly used for the protection of power receiving and distributing equipment.
2. Description of the Related Art
FIG. 3 shows an example of a prior art vacuum circuit breaker. In this Figure, 41 is an interrupting unit, and 50 is an operating mechanism unit. Interrupting unit 41 includes a plurality (only one shown in the drawing) of vacuum interrupters 43 arranged in a box-shaped insulating casing 42. Vacuum interrupter 43 incorporates a fixed electrode and a movable electrode that can be moved up against or separated from the fixed electrode. A fixed rod mounted on this fixed electrode is fixed to a top end plate 44. A movable rod 46 mounted on the movable electrode is mounted movably in the axial direction on a bottom end plate 45 by means of a bellows. Respective main circuit isolator units 47a, 47b of the fixed electrode and movable electrode are connected from these electrodes to the outside of the insulating casing 42. 48 is an insulating rod linked to movable rod 46. A linkage mechanism, not shown, of operating mechanism unit 50 is assembled within frame 51 that is unitary with a truck. Only parts subsequent to (or downstream of) an output level 52 which constitute parts of the linkage mechanism, are shown in the Figure. An output lever 52 is rotatably mounted on frame 51 by means of a main shaft 53. Its other end is linked to one end of a connecting rod 54 which is assembled with a contacts pressurizing spring 55. The other end of connecting rod 54 is linked to the drive end of a drive lever 57 which is rotatably mounted by means of a support shaft 56. The working end of drive lever 57 is linked to the bottom end of insulating rod 48. The rated voltage of the vacuum circuit breaker can be altered by changing the separation between the fixed and movable electrodes within vacuum interrupter 43 i.e. by changing the contact gap. Adjustment of this contact gap is effected by altering the length of drive lever 57.
Thus, when a circuit-making instruction is applied from outside, the linkage mechanism in operating mechanism unit 50 is actuated to turn output lever 52 in the clockwise direction, driving connecting rod 54 downwards so that contacts pressurizing spring 55 is compressed and drive lever 57 is rotated in the counter-clockwise direction. As a result, movable rod 46 is driven upwards by means of insulating rod 48 so that the movable electrode contacts the fixed electrode, thereby closing the electrodes of vacuum interrupter 43. This electrodes-closed condition is maintained by the resilient force provided by contacts pressurizing spring 55.
In the contrary process, when an open-circuit instruction is supplied from outside, releasing a trip catch, not shown, incorporated in operating mechanism unit 50, output lever 52 is rotated counter-clockwise by the restoring force of contacts pressurizing spring 55 etc., thereby causing drive lever 57 to be rotated in the clockwise direction. As a result, movable rod 46 is moved downwardly and the electrodes of vacuum interrupter 43 are opened.
A further prior art example is shown in FIG. 4. In this prior art example, operating mechanism unit 50A is incorporated at the bottom of interrupting unit 41 and a contacts pressurizing spring 58 is provided on part of a connecting rod that connects the other end of output lever 52 and the bottom end of insulating rod 48.
In the prior art example of FIG. 3, since contacts pressurizing spring 55 is provided in the vertical direction between the other end of output lever 52 and the drive end of drive lever 57, in operating mechanism unit 50, the height of operating mechanism unit 50 is raised by the length of contacts pressurizing spring 55. This is one factor that increases the dimensions of operating mechanism unit 50. A further problem was that, if the size of the contacts gap was increased in order to raise the rated voltage, since this increases the length of drive lever 57, the size of the vacuum circuit breaker is increased.
Furthermore, since contacts pressurizing spring 55 is separated from support shaft 56 by a certain distance, the moment of contacts pressurizing spring 55 is added to the rotational moment of drive lever 57. This is a factor that delays the speed of opening and closing of the contacts.
In the prior art example of FIG. 4, since contacts pressurizing spring 58 is provided vertically between the other end of output lever 52 and the bottom end of insulating rod 48 in operating mechanism unit 50A, the height of breaker unit 41 is raised by the length of contacts pressurizing spring 58. This is one factor that increases the dimensions of the vacuum circuit breaker as a whole.